You should have created your own thread for this, sadaf1230.
With that said, unless you are an electronics mechanic (and if you were, then you wouldn't be asking this question) there is nothing you can do about it-- you have a bad slot or memory manager chip on the motherboard and neither are replaceable by the average Joe (nor the above-average Joe: I have the equipment and skills due to my career, but it is impractical and the chance of success is low).
In my mind, this is the technology God giving you the signal that it is time for an upgrade.